Overhead doors are used to occlude openings in structures such as warehouses, factories, and other commercial establishments. Doors are typically used at loading docks and are often subject to impacts from fork lifts, other loading devices, and freight. Such impacts often cause damage to an overhead door and sometimes to the building structure supporting the door. A variety of impact-resistant doors have been developed in response to this problem. For example, U.S. Pat. No. 5,584,333, issued to Torchetti et al., and U.S. Pat. No. 5,025,847, issued to Mueller, disclose assemblies designed to lessen the damage caused by an impact to a door.
While these and other prior-art devices have operated with some degree of success, they have several shortcomings. The impact resistant assemblies shown in U.S. Patent No. 5,025,847, while operable to release from an associated track upon being exposed to force of a predetermined magnitude, are relatively complex in their mechanical arrangement. Complex door designs, of course, greatly increase the cost of manufacturing and maintaining an overhead door. Further, the door design taught by U.S. Pat. No. 5,584,333, while useful for reducing the damage to a flexible, bottom panel, is not appropriate for all applications, particularly those where a door with relatively rigid panels is desired.
A further shortcoming with the various prior-art devices is the difficulty and sometimes impossibility of replacing panels in the doors after they have been damaged by an impact. Even in doors designed to lessen or reduce damage caused by impacts, door panels can become damaged to a point where they are inoperable. Typically, replacing a panel requires installing an entirely new door or completely releasing spring tension, disconnecting counterbalance cables, and panel hardware, and removing the door from its tracks in order to replace the damaged panel.
Another shortcoming with prior-art doors is that they are constructed from relatively costly materials. For example, the door shown in U.S. Pat. No. 5,535,805, issued to Kellogg et al., includes extruded plastic tracks which are made from a relatively expensive low-friction material. In addition, the panels used in the door are made from numerous parts and relatively expensive non-metallic materials, including polycarbonate and fiberglass. While these doors are robust, many customers can't afford and don't desire such an expensive, heavy-duty door.
Therefore, it would be desirable to have an improved overhead door designed so that its panels could be readily replaced without the need to remove the entire door from its tracks. Further, it would be desirable to have a door that releases from its tracks when exposed to a force of a predetermined magnitude in order to limit or prevent damage to the door, its track, and surrounding structure. Further, it would be desirable if the door had a simple design with relatively few components which could be manufactured from relatively inexpensive materials so as to reduce the overall cost of the door.